Smith also studied the carbon dioxide expired during work on a treadmill having 43 steps, ascending 28.65 feet per minute, the carbon dioxide being determined for short periods of a few minutes each. The after-effect of the muscular work is excellently shown by the fact that the pulse-rate during Smith's work experiment of October 9 was 150, and after 29 minutes of rest it was 102 beats per minute, while his pulse-rate in a period of rest was as a rule considerably under 88; furthermore, even after 29 minutes of rest, 9.14 grains of carbon dioxide were given off per minute as compared with approximately 6 grains during rest before work.

Using the large respiration chamber at Munich, Pettenkofer and Voit " made a number of experiments on men at rest and with muscular work. For a subject they employed a man who had been accustomed to using a foot-power lathe, and the resistance of the apparatus was so adjusted as to correspond to his daily work. The man worked 9 hours each day. The workperiods were compared not only with ordinary rest-periods, but with restperiods in which the subject fasted. Thus, in a series of three 24-hour fasting experiments, the subject gave off during the first two days of rest 738 and 695 grams of carbon dioxide respectively, while on the third day, which was a work-day, he gave off 1,187 grams. In another series, in which the work followed rest with food, the results for the first three days of rest were 912, 943, and 930 grams of carbon dioxide respectively, while those for the two working-days were 1,285 and 1,134 grams of carbon dioxide respectively. The apparatus used did not permit direct measurements of oxygen, and although the investigators computed the oxygen consumption, their computations were subsequently shown by Voit to contain errors.

b

In 1881 Voit reported two other experiments in which the subject worked without food, but no statement as to the method by which the work was performed was given. In the first experiment the work lasted 5 hours, corresponding to 29,529 kilogrammeters per hour. According to Voit, this called for an increase in the metabolism of 9.1 grams of fat per hour. A second man weighing 60 kilograms, likewise without food and working under exactly the same conditions, performed in an hour 19,036 kilogrammeters of work, requiring an increased decomposition of 7.2 grams of fat. Averaging the results of these two experiments, Voit computed that a load or task necessitating 24,282 kilogrammeters of work in an hour resulted in an increased decomposition of 8.2 grams of fat, this being equivalent to a production of 23.0 grams of carbon dioxide.

As early as 1866 Speck, employing a new design of respiration apparatus in which the expired air was collected in a spirometer and then analyzed, made a number of experiments with muscular work. In these experiments, which lasted from 6 to 9 minutes, both the carbon-dioxide production and the oxygen consumption were determined. The muscular work consisted in raising a weight by the bent arm to a given distance, the weight and height being used for the computation of the amount of work performed in kilogrammeters. In 1871 a second series of experiments was made in which the weight was raised as before, but was lowered by an assistant. The experimental periods averaged about 4 minutes.

a Pettenkofer and Voit, Zeitschr. f. Biol., 1866, 2, p. 459.

b Voit, Hermann's Handbuch der Physiologie, Leipsic, 1881, 6, part 1, p. 202.

c Speck, Physiologie des menschlichen Athmens, Leipsic, 1892.

In 1885 Speck made another series of experiments, using a form of ergometer in which a wheel was turned by the hand, the friction being adjusted by means of a screw. In these experiments, which were but 2 to 3 minutes in length, both the carbon-dioxide production and the oxygen consumption were determined.

b

Speck's results were published in a number of papers, but were later collected by him into one volume." His results have also been given in abstract by Sondén and Tigerstedt with special reference to the carbon-dioxide production. Speck noticed distinctly the after-effect of work, and it is obvious that his experiments at work are vitiated by the fact that since they lasted but 2 or 3 minutes, the carbon dioxide excreted during the first part of the experiment was unquestionably not so great as would result from the amount of work carried out during that period.

Employing a unique form of respiration apparatus, Hanriot and Richet made a number of experiments in 1887, in which the work was performed either by turning a wheel or raising a weight. Their respiration apparatus, although extraordinarily ingenious, had practical disadvantages which have deterred physiologists as a whole from employing it. In fact, many of the experiments reported by these investigators have been the subject of severe criticism.

The effect on the excretion of carbon dioxide of the muscular activity of climbing was studied in Kronecker's laboratory, in August 1888, by Gruber, who made experiments in which he climbed a distance of 81.55 meters, the last 31.55 meters being in a tower. Experiments were also made in which a 15-kilogram weight was carried as a load; the effect of practice was likewise studied. The carbon dioxide was determined by absorption with soda-lime, the kilogrammeters of work performed being computed from the bodyweight and the height ascended.

Schnyder, of Kronecker's laboratory, made further studies on the influence of muscular activity, employing for the purpose a peculiar form of wheel by means of which large blocks of stone could be lifted by the bodyweight of the subject. The carbon dioxide was absorbed by soda-lime as in Gruber's experiments, and the work performed could be computed, due allowance being made for the friction of the wheel and chain. Experiments were also made with an apparatus on the treadmill principle devised by Professor Kronecker.

In addition to the investigations previously cited in which the effect of muscular activity upon metabolism was studied, a considerable number were carried out by means of special forms of apparatus. These may conveniently be classified according to the method employed into three groups, i. e., the investigations of Zuntz and his associates, in which the Zuntz-Geppert apparatus was used; the investigations carried out in the French laboratories with apparatus devised by Chauveau and Tissot; and investigations in which the chamber method was employed, including especially those made by Sondén and Tigerstedt, by Rubner, and by Atwater and his associates.

a Speck, loc. cit., pp. 56-95.

Sondén and Tigerstedt, Skand. Archiv f. Physiol., 1895, 6, p. 1.

Hanriot and Richet, Comptes rendus, 1887, 105, p. 76.

d Gruber, Ztschr. f. Biol., 1891, 28, p. 466. The experiments were reported before the Schweizerischen Naturforscherversammlung in Solothurn; a notice with regard to them was also published in October 1888 in the Correspondenz-Blatte für Schweizer Aerzte.

e Schnyder, Zeitsch. f. Biol., 1896, 33, p. 289.

INVESTIGATIONS BY ZUNTZ AND HIS ASSOCIATES.

The first extensive investigation on the effect of muscular work upon metabolism carried out by means of the Zuntz-Geppert apparatus was that reported by Katzenstein." The work consisted of moving a Gaertner ergostat with the arm, and walking on a level and also on an inclined plane by means of a treadmill designed by Lehmann and Zuntz. The experiments were for the most part of very short duration — only 4 to 6 minutes. Katzenstein found no material alteration in the respiratory quotient, notwithstanding the increased metabolism. He also made a series of observations on the aftereffect of work upon metabolism.

In 1898 Leo Zuntz published a description of a series of experiments made with a Zuntz apparatus for studying the metabolism during bicycle riding. The work performed was sufficient to produce 9 times the amount of carbon dioxide excreted during rest. This series of experiments represents the first careful attempt to study the metabolism during bicycle riding.

The effect of different diets upon muscular work was studied in a long series of experiments, 176 in number, by Frentzel and Reach. The work was performed on a treadmill in the Zuntz laboratory. Inasmuch as this is the first time that an extensive investigation was made on the effect of muscular work upon the character of the katabolism, we shall have occasion to refer to it frequently on subsequent pages.

e

In 1901 Heinemann reported a series of experiments performed in Zuntz's laboratory, in which the Gaertner ergostat and the Zuntz-Geppert apparatus were likewise used. In these experiments special attention was also given to the effect of different diets upon the amount of muscular work, and upon the quantity and quality of the material burned during muscular activity. The muscular work, which was approximately constant in all the experiments, averaged 360 kilogrammeters per minute.

A practical application of the study of muscular work as influencing the metabolism was made by Reach in the laboratory of Durig in Vienna. Reach used for the muscular work the turning of a centrifugal milk-separator which had been carefully calibrated by an electrically-driven motor. The gaseous metabolism was determined by the Zuntz-Geppert apparatus and compared with the amount of external muscular work performed. From his results he then computed the calories per kilogrammeter in turning the wheel of the machine, and compared his results with similar body-activity observed by Katzenstein, Sondén and Tigerstedt, Johansson and Koraen, and Hanriot and Richet.

In connection with their study of the fasting metabolism of a subject (Breithaupt) who fasted 6 days, Lehmann and Zuntz made observations on the effect of muscular work, using the Gaertner ergostat and collecting the gas samples in short periods, namely, from 2 to 5 minutes. Their observations also included data with regard to the after-effects of work.

a Katzenstein, Pflüger's Archiv f. d. ges. Physiol., 1891, 49, p. 330.

b Leo Zuntz, Pflüger's Archiv f. d. ges. Physiol., 1898, 70, p. 346.

Frentzel and Reach, Pflüger's Archiv f. d. ges. Physiol., 1901, 83, p. 477.

d The treadmill used is described in the Landw. Jahrb., 1889, 28, p. 7.

e Heinemann, Pflüger's Archiv f. d. ges. Physiol., 1901, 83, p. 441.

Reach, Landw. Jahrb., 1908, 37, p. 1053. See also Biochem. Zeitschr., 1908, 14, p. 430.
Lehmann and Zuntz, Archiv f. path. Anat. u. Physiol., 1893, 131, supp., p. 92.

Among the methods used for measuring the amount of muscular work performed in connection with respiration experiments, mention should be made of a form of ergostat devised by Jaquet and described by H. Christ." As the subject stepped upon this machine, the height of each step could be measured, and the total height multiplied by the body-weight gave the total amount of muscular work performed. The studies made by Jaquet and Svenson' with this ergostat consisted of experiments with fat individuals in which the Zuntz-Geppert respiration apparatus was used to measure the gaseous metabolism. Jaquet also studied the after-effects upon the respiratory exchange of muscular work incidental to mountain-climbing, using a ZuntzGeppert apparatus. He later repeated these experiments with a Speck apparatus and a spirometer containing 100 liters."

Finally, in any résumé of the work done by Zuntz and his associates, mention should be made of the interesting experiments of Kolmer on swimming. During these experiments he found that the oxygen consumption was increased over that during resting 9 times, nearly 20 per cent greater than the amount required for rapid mountain-climbing, thus showing the enormous metabolism during the operation of swimming.

The active interest of Zuntz and his associates in the metabolism during marching and mountain-climbing has resulted in a large number of contributions on this subject from Zuntz' laboratory and from Durig. The difficulties incidental to computing the amount of external muscular work performed in climbing mountains are obvious, but the observations with the treadmill are of direct mathematical value. The results of the investigations made by Zuntz and other workers who used the Zuntz-Geppert apparatus have been admirably brought together in a number of publications.

INVESTIGATIONS IN THE FRENCH LABORATORIES.

Investigations in the French laboratories on the question of muscular activity and metabolism have been carried out extensively by Chauveau, Tissot, Laulanié, and, more recently, by Amar. Chauveau in 1899 repeated the experiments of Hirn, using a treadwheel and determining directly the heat radiated from the body. The emission calorimeter was used, and no correction was made for the heat of water vaporized. The air was collected in a Tissot spirometer, the samples being taken in 3 periods of 2 minutes each" at the beginning, middle, and end of the experiment. Since the calorimetric measurements were made during the last part of the experiment, only those results obtained from the analyses of the samples collected in the last period should be used for comparison with the calorimetric measurements. Although dealing exclusively with the respiratory quotient, i. e., the character of the

a Christ, Deutsch. Archiv f. klin. Med., 1894, 53, p. 102.

b Jaquet and Svenson, Zeitschr. f. klin. Med., 1900, 41, p. 17. Jaquet, Archiv f. exp. Path. u. Pharm., 1910, 62, p. 341.

d Zuntz, Loewy, Müller, and Caspari, Höhenklima u. Bergwanderungen, Berlin, 1906, p. 263.

e Zuntz, Loewy, Müller, and Caspari, Ibid. Durig, Physiol. Ergebnisse der im Jahre 1906 Durchgeführten Monte Rosa Expedition. Besonders Abgedruckt aus dem LXXXVI Bd. Denkschriften der Mathematisch-Naturwissenschaftlichen Klasse der Kaiserlichen Akademie der Wissenschaften, Wien. 1 Zuntz, Loewy, Magnus-Levy, and others in Oppenheimer's Handbuch der Biochemie. Zuntz and Schumberg, Physiologie des Marsches, Berlin, 1901. Magnus-Levy, Physiologie des Stoffwechsels, in von Noorden's Handbuch der Pathologie des Stoffwechsels, Berlin, 1906, 1, p. 379.

Chauveau, Comptes rendus, 1899, 129, p. 249.

For a criticism of the length of the experiments see Weiss, Physiologie générale du travail musculaire et de la chaleur animale, Paris, 1909, p. 142.

katabolism, the experiments on Tissot reported by Chauveau" should be cited. The work was done by going up and down stairs, and the gaseous exchange studied by the Chauveau-Tissot apparatus.

с

Laulanié's experiments were made chiefly with animals, but Amar in 1910 studied the effect of bicycling upon the metabolism of men. Using a bicycle ergometer, the Chauveau-Tissot valves, and a dry gas-meter, he made experiments on the natives in Algeria, collecting and analyzing samples of the expired air. In his observations special emphasis was laid upon a study of the mechanical efficiency of the body as a machine. These values will be referred to subsequently. Amar's monograph contains an excellent résumé of the earlier literature with particular emphasis upon the work carried out in the French laboratories. The percentage of efficiency is given special treatment.d

A later research of Amar deals with the muscular work involved in filing a piece of metal. With a most ingenious arrangement of tambours and dynamometer springs Amar made a series of experiments both with an apprentice and a skilled machinist. A study of the gaseous exchange was made in many of the experiments. As was to be expected with this form of work low efficiencies were found.

INVESTIGATIONS BY THE CHAMBER METHOD.

The principal investigations on muscular work by the chamber method were made by Sondén and Tigerstedt in Stockholm, Rubner in Berlin, and Atwater and his associates in Middletown, Connecticut.

Employing the large Sondén-Tigerstedt respiration chamber in the Karolinska Institute in Stockholm, Sondén and Tigerstedt carried out a series of investigations studying only the effect of muscular work upon the carbon-dioxide output, their apparatus not being designed for determining the oxygen consumption. Several forms of muscular activity were used, the study including experiments in which the subject walked about the chamber, the distance traveled being measured by means of a pedometer, and experiments in which the subject climbed up and down a ladder placed inside the chamber. The Gaertner ergostat and the Fick dynamometer were also employed. In reporting these researches, Sondén and Tigerstedt computed the results obtained by earlier workers with reference to the relationship between the carbon-dioxide production and muscular activity so as to make them comparable with their own results. This comparison is given in table 3, which is taken from the report of Sondén and Tigerstedt."

Using a special form of ergostat, in which the arms and muscles of the back were employed, Johansson" made a series of experiments in which he raised a weight to a given distance, the amount of work ranging from 600 to 7,000 kilogrammeters. Placing the apparatus inside the Sondén-Tigerstedt respiration chamber, he determined the carbon-dioxide production for each kilogrammeter of external muscular work, concluding from his results that

a Chauveau, Comptes rendus, 1896, 122, p. 1163. Laulanié, Éléments de physiologie, 2d ed., Paris, 1905.

Amar, Le rendement de la machine humaine. Recherches sur le travail, Paris, 1910.

d See also Weiss, loc. cit.

e Amar, Journal de Physiologie et de Pathologie generale, 1913, 15, pp. 69 and 102.

Sondén and Tigerstedt, Skand. Archiv, 1895, 6, p. 1.

Sondén and Tigerstedt, loc. cit., p. 202.

h Johansson, Skand. Archiv, 1901, 11, p. 273.